1. Field of the Invention
The present invention relates to nonreciprocal circuit devices, and in particular, to a nonreciprocal circuit device such as an isolator or a circulator for use in microwave bonds, and a communication apparatus including the nonreciprocal circuit device.
2. Description of the Related Art
In general, a lumped-constant isolator for use in a mobile communication apparatus such as a mobile phone has a function of allowing signals to pass only in a transmission direction so that a reverse transmission of the signals is prevented. As for conventional mobile communication apparatuses, a reduction in thickness and weight is in great demand, due to their uses.
A lumped-constant isolator of the above type includes a permanent magnet, a ferrite member to which a direct current magnetic field is applied by the permanent magnet, a plurality of central electrodes arranged on the ferrite member, a resistor element, a resin case for accommodating the ferrite member, the central electrodes, and the resistor element, and a metal case for accommodating the permanent magnet, the ferrite member, and the central electrodes.
In general, an isolator is often formed such that a permanent magnet is provided to cover the entire surfaces of a ferrite member and a resistor element so that the isolator exhibits its performance to the maximum. In the case of a conventional isolator, the upper surface of a resistor element provided in a resin case is above the upper surface of an insulating spacer on a ferrite member and a matching capacitor. Thus, the total of the thicknesses of the permanent magnet and the resistor element determines the overall height of the isolator.
In actuality, in accordance with the total of the thicknesses or the resistor element and the permanent magnet, by increasing the thickness of the insulating spacer to be more than a value that is essentially required, the upper surface of the insulating spacer is level with the height of the resistor element. This is because the permanent magnet is stably and horizontally disposed in the isolator. Here, it is possible that the thickness of the permanent magnet be reduced. This causes a problem in that the magnitude of a direct current magnetic field which is applied to the ferrite member is insufficient, so that a reduction in thickness is difficult.
Accordingly, it is an object of the present invention to provide a nonreciprocal circuit device having a height reduced without reducing the thickness or a permanent magnet, and a communication apparatus including the nonreciprocal circuit device.
To this end, according to an aspect of the present invention, the foregoing object is achieved through provision of a nonreciprocal circuit device including a permanent magnet; a ferrite member to which a direct current magnetic field is applied by the permanent magnet, said ferrite member including a plurality of central electrodes; a resistor element which has a thickness of not less than 0.1 mm and not greater than 0.5 mm and in which a resistor is provided between lead electrodes formed on two ends of a main surface of a substrate; a resin case for accommodating the ferrite member, the central electrodes, and the resistor element; and a metal case for accommodating the permanent magnet, the ferrite member, and the central electrodes.
The above-described construction enables a nonreciprocal circuit device to have a low height without reducing the thickness of the permanent magnet.
By allowing the lead electrodes in the resistor element to extend on two sides of the substrate or to extend to the other main surface of the substrate via the two sides, an area of contact between the lead electrodes in the resistor element and terminals provided on the resin case is increased. This increases the strength of bonding by solder or the like, and reliability is enhanced.
According to another aspect of the present invention, a communication apparatus includes a nonreciprocal circuit device having the above-described characteristics, whereby the thickness of the communication apparatus is reduced. This provides high reliability.
Since the thickness of a resistor element is reduced to not less than 0.1 mm and not greater than 0.5 mm, the height of a nonreciprocal circuit device can be reduced without reducing the thickness of a permanent magnet. In addition, since lead electrodes in the resistor element are provided to extend on two sides of one main surface of a substrate or to extend to the other main surface of the substrate via the two sides, an area of contact between the lead electrodes in the resistor element and terminals provided on the resin case is increased. Accordingly the strength of bonding by solder or the like can be increased enhancing reliability. As a result, a highly reliable thin nonreciprocal circuit device and a communication apparatus having the nonreciprocal circuit device are obtained.